AASHTO
– American Association of State Highway and Transportation
Officials

Absolute Viscosity –
A measure of the Viscosity of Asphalt Cement with respect
to time, measured in poises, conducted at 60°C (140°F).
The test method utilizes a partial vacuum to induce flow
in the viscometer.

Acceptance – Sampling
and testing, or inspection, to determine the degree of
compliance with contract requirements for acceptance,
rejection, or Pay Adjustment.

Aggregate Storage Bins or Cold
Feed Bins – Bins that store the necessary
Aggregate sizes and feed them to the Dryer in a Hot Mix
Plant in substantially the same proportions as are required
in the finished mix.

Air Voids – The
amount of air in a compacted Asphalt Concrete mixture,
expressed as a percentage of the total volume of the mixture.

Alligator Cracking –
The occurrence of interconnected Cracks forming a series
of small blocks resembling an alligator's skin or chicken-wire
and caused by excessive deflection of the surface over
unstable Subgrade or lower courses of the pavement.

Ambient
Grinding – A grinding method for processing
scrap tires into crumb rubber by passing the tires through
a series of grinders at ambient temperatures. Ambient
Grinding produces crumb rubber particles with a very rough,
sandpapery surface texture.

Anti-oxidant
– Any material that slows the oxidation reaction
(aging).

Asphalt – See Asphalt
Cement.

Asphalt
Binder – Asphalt Cement used in paving
applications that has been classified according to the
Standard Specification for Performance Graded Asphalt
Binder, AASHTO Designation MP1. It can be either unmodified
or modified Asphalt Cement, as long as it complies with
the specifications.

Asphalt Cement or Asphalt
– A dark brown to black cementitious material in
which the predominating constituents are Bitumens, which
occur in nature or are obtained in petroleum processing.
Asphalt Cement is a constituent in varying proportions
of most crude petroleum and is used for paving, roofing,
industrial and other special purposes. It is a semi-solid
at room temperature and a liquid at hotter temperatures.

Asphalt
Concrete - A mixture of Asphalt Binder and Aggregate
used as a paving material, which is thoroughly mixed and
compacted to form a pavement layer.

Asphalt Concrete Overlay
- One or more courses of Asphalt Concrete placed over
an existing pavement.

Asphalt Content –
The amount of Asphalt Binder in an Asphalt Concrete mixture,
expressed as a percentage of the weight of the total mix
(Coarse Aggregate, Fine Aggregate, Asphalt Binder, Mineral
Filler, lime, fibers, etc.).

Asphalt Emulsion - An emulsion of Asphalt
Binder, water, and a small amount of an Emulsifying Agent
(soap) to give it a liquid consistency at ambient temperatures
so that it can be sprayed on a road surface. Once the
water begins to evaporate, the Asphalt Emulsion “breaks”,
leaving the sticky Residual Asphalt Binder behind. Emulsified
Asphalt Binder droplets may have a positive surface charge,
a negative surface charge, or no surface charge (neutral).

Asphalt Mat – The
term used to refer to the Asphalt Concrete layer when
it is still hot during placement and Compaction operations.

Axial Stress –
Pressure resulting from the application of force along
the object’s central axis.

Base Course
- The layer in the Pavement Structure immediately below
the Surface and/or Intermediate Courses and immediately
above the Subgrade and/or Subbase Course. It usually consists
of crushed stone, although it may consist of crushed slag
or other stabilized or un-stabilized material.

Batch Plant – A
type of Hot Mix Plant that manufactures HMA in batches
rather than continuously and is more suited for small
manufacturing runs and (frequent) changes in mixture types.

Bending Beam
Rheometer (BBR) – A piece of laboratory
equipment used in the AASHTO TP1 procedure to evaluate
Asphalt Binder properties at low pavement temperatures
by measuring how much a binder Deflects, or creeps, under
a constant load at a constant temperature. This test provides
insight into a binder’s resistance to thermal, or
low-temperature, cracking. The BBR test temperatures are
related to a pavement’s lowest service temperature,
and when its results are used in conjunction with results
from the DSR, it can provide the stiffness behavior for
Asphalt Binder over a wide range of temperatures.

Bitumen - A class of
black or dark-colored (solid, semisolid, or viscous) cementitious
substances, natural or manufactured, composed principally
of high molecular weight hydrocarbons, of which Asphalts,
tars, pitches, and asphaltites are typical.

Bleeding or Flushing
- The upward migration of Asphalt Binder in an Asphalt
Concrete pavement resulting in the formation of an Asphalt
Binder film on the pavement surface.

Brittle – Describes
a material with the tendency to fracture (break) without
much stretching.

Breaking - The phenomenon
when Asphalt Binder and water separate in an Asphalt Emulsion
beginning the Curing process. The rate of Breaking is
controlled primarily by the Emulsifying Agent, although
it is also somewhat dependent on environmental conditions.

Bulk Specific Gravity (BSG or
Gmb) – In the context of Asphalt Concrete
mixtures, the Specific Gravity of a compacted sample from
the mix design or the finished pavement.

Compaction
– The act of increasing the Density of HMA by applying
a specific amount of loading. In the lab, this is done
with a Marshall hammer or a Superpave Gyratory Compactor.
In the field (during construction of the pavement), this
is done with various combinations of Steel-wheel and Rubber-tired
Rollers.

Complex Shear Modulus (G*)
– A measure of the total resistance of a material
(in this case, Asphalt Binder) to Deformation when exposed
to repeated pulses of Shear Stress. It consists of a recoverable
(elastic) component and a non-recoverable (viscous) component.
For Asphalt Binder, this is highly dependent upon the
temperature and frequency of loading.

Corrugation or Shoving
- A form of permanent Deformation typified by ripples
across the pavement surface. These Distortions usually
occur at points where traffic starts and stops, on hills
where vehicles break on the downgrade, on sharp curves,
or where vehicles hit a bump and bounce up and down.

Crack
- An approximately vertical random cleavage of the pavement
caused by traffic loading, thermal stresses, and/or aging
of the Asphalt Binder.

Creep - Gradual Deflection
under a constant load applied at a constant rate. With
respect to the Bending Beam Rheometer test for Asphalt
Binder, Creep loading simulates the thermal stresses that
gradually build up in a pavement when temperature drops.

Crumb Rubber
Modifier (CRM) - The term used to describe ground
waste tire rubber used in Hot Mix Asphalt and other paving
applications.

Crusher-Run - The unscreened
raw product of a stone crusher.

Cryogenic
Grinding – A grinding method for processing
scrap tires into crumb rubber by freezing the tires with
liquid nitrogen and then passing them through hammer mills
where they are shattered into small particles. Cryogenic
Grinding produces crumb rubber particles with a very smooth,
glasslike surface texture.

Curing – In reference
to an Asphalt Emulsion, it is the development of the mechanical
properties of the Asphalt Binder after the Asphalt Emulsion
has “broken” and the Residual Asphalt Binder
bonds to the underlying HMA surface and the cover Aggregate
or the Asphalt Concrete Overlay. In reference to PCC,
it is the development of rigidity resulting from the hydration
reaction occurring in the Portland Cement paste.

Cutback Asphalt - Asphalt
Binder that has been liquified by blending with petroleum
solvents (diluents). Upon exposure to atmospheric conditions,
the diluents evaporate, leaving behind the Residual Asphalt
Binder to perform its function. Cutback Asphalts are rarely
used anymore because they are not environmentally-friendly.

Deflection
- A load-induced, downward movement of a pavement section.

Deformation – See
Distortion

Delta – See Phase
Angle

Dense-graded HMA –
HMA made with a Dense-graded aggregate blend. Dense-graded
aggregate has approximately equal proportions of Coarse,
medium-sized, and Fine Aggregate particles that can fit
closely together when compacted. Although it is possible
for Dense-graded HMA to have the same percentage of air
voids as Gap-graded HMA, the distribution of voids is
very different. Dense-graded HMA has many small voids,
while Gap-graded HMA has a few large voids.

Density – The ratio
of a substance’s weight compared to its volume (weight
per unit volume), often expressed in pounds-per-cubic-foot
(pcf) or grams-per-cubic-centimeter (g/cc). In the context
of Asphalt Concrete pavement, Density is increased by
reducing the amount of air in the pavement layer through
Compaction processes.

Design ESAL - The total
number of Equivalent 80-kN (18,000-lb.) Single Axle Load
(ESAL) applications expected throughout the Design Period.

Design Lane - The lane
on which the greatest number of Equivalent 80-kN (18,000-lb.)
Single Axle Loads (ESAL) is expected. This will normally
be either lane of a two-lane roadway or the outside lane
of a multi-lane highway.

Design Period - The number
of years from the initial application of traffic until
the first planned major resurfacing or overlay. This term
should not be confused with pavement life or analysis
period. Adding Asphalt Concrete Overlays as required will
extend pavement life indefinitely or until geometric considerations
(or other factors) make the pavement obsolete.

Direct Tension
Tester (DTT) - A piece of laboratory equipment
used in the AASHTO TP3 procedure to discover an Asphalt
Binder’s ability to stretch before breaking. The
DTT procedure is performed at very low temperatures, where
binders generally exhibit Brittle rather than Ductile
behavior. In addition, the binders tested are aged with
both the RTFO and the PAV, which also increase Brittle
tendencies. The DTT measures the amount of elongation
per unit length (strain) exhibited by a “dog bone”
shaped (wide on each end and narrow in the middle) Asphalt
Binder specimen before breaking (failure). Like the BBR,
the DTT also provides insight into a binder’s ability
to resist thermal (low-temperature) cracking.

Disintegration - The
breaking up of a pavement into small, loose fragments
caused by traffic or weathering.

Distortion or Deformation
– Any change of a pavement surface from its original
shape.

Drum Mix Plant - A type
of Hot Mix Plant that proportions the aggregate, then
dries and coats the Aggregate with a proportional amount
of Asphalt Binder in the same drum. Drum Mix Plants produce
HMA continuously rather than in batches and are more suited
for long runs of the same product.

Dryer - An apparatus
that will dry the Aggregates and heat them to the specified
temperatures.

Ductility - The ability
of a substance to be drawn out or stretched thin without
breaking. While Ductility is considered and important
characteristic of Asphalt Cements in many applications,
the presence or absence of Ductility is usually considered
more significant than the actual degree of Ductility.

Durability - The property
of an Asphalt Concrete pavement that represents its ability
to resist Disintegration by weathering and traffic.

Dynamic Shear
Rheometer (DSR) – A piece of laboratory
equipment used to perform the AASHTO TP5 procedure on
un-aged, RTFO-aged, and PAV-aged Asphalt Binders. In the
DSR, a small disc-shaped sample of Asphalt Binder is sandwiched
between two plates, one of which is fixed, and the other
of which is oscillating. The DSR measures the Complex
Shear Modulus and Phase Angle at intermediate and high
temperatures, which can be used to predict resistance
to Rutting and Fatigue Cracking in Asphalt Concrete pavements
made with the Asphalt Binder being tested.

Edge Joint
Cracks - The separation of the joint between
the pavement and the shoulder, commonly caused by the
alternate wetting and drying beneath the shoulder surface.
Other causes are shoulder settlement, mix shrinkage, and
trucks straddling the joint.

Emulsifying Agent or Emulsifier
- The chemical added to the water and Asphalt Binder that
keeps the droplets of Asphalt Binder in stable suspension
in the water. The Emulsifier determines the charge of
the Asphalt Emulsion and controls the Breaking rate.

Equivalent Single Axle Load (ESAL)
- The effect on pavement performance of any combination
of axle loads of varying magnitude equated to the number
of 80-kN (18,000-lb.) single-axle loads that are required
to produce an equivalent effect.

Flexibility - The ability
of a pavement to conform to settlement of the foundation
without fracturing. Generally, high Asphalt Binder content
or the use of Rubber-modified Asphalt Binder enhances
the flexibility of Asphalt paving mixtures.

Fog Seal - A light application
of diluted Asphalt Emulsion. It is used to renew old asphalt
pavement surfaces, seal small cracks and surface voids,
and inhibit Raveling.

Full-depth Asphalt Pavement
– A Pavement Structure that is designed and constructed
so that all courses above the Subgrade are Asphalt Concrete.
A Full-Depth Asphalt Pavement is placed directly on the
prepared Subgrade.

G*
- See Complex Shear Modulus

Gap-graded HMA
– HMA made with a gap-graded aggregate blend. Gap-graded
aggregate has large proportions of Coarse and Fine Aggregate
particles, but a very small proportion of medium-sized
Aggregate particles. This particle-size distribution exhibits
a great deal of stone-on-stone contact between the Coarse
Aggregate particles. Although it is possible for Gap-graded
HMA to have the same percentage of air voids as Dense-graded
HMA, the distribution of voids is very different. Gap-graded
HMA has a few large voids, while dense-graded HMA has
many small voids.

Gyratory Compactor –
A type of lab compactor used in the Superpave method of
HMA mix design or for compacting samples of hot mix asphalt
into specimens used for volumetric analysis for Quality
Control activities at the Hot Mix Plant. It compacts samples
of HMA with a kneading motion caused by a set pressure
and angle of gyration while continuously recording sample
height measurements.

Hot Aggregate
Storage Bins - Bins that store heated and fractionated
Aggregates prior to their final proportioning into the
Hot Mix Plant.

Hot Mix Asphalt
(HMA) - A form of Asphalt Concrete that is mixed
at a contractor’s Hot Mix Plant, transported to
the roadway in dump trucks, placed using a paver, and
compacted with Steel-wheel or Rubber-tired Rollers.

Hot Mix Plant or Hot Mix Asphalt
(HMA) Plant – A manufacturing facility
that produces Asphalt paving mixtures by heating the ingredients
(Aggregate, Hydrated Lime, Asphalt Binder, and sometimes
other modifiers), combining them in the correct proportions,
and blending them to form a homogeneous mixture. It can
be either a Batch Plant or a Drum Plant.

Indirect Tensile
Strength (ITS) – Test procedure to examine
Asphalt Concrete mixtures for Moisture Susceptibility.
The ITS value is measured on both dry samples and samples
that have been exposed to heat and moisture. The “dry”
and “wet” ITS values are then used to calculate
the TSR.

Kinematic
Viscosity - A measure of the Viscosity of Asphalt
Cement, measured in centistokes, conducted at a temperature
of 135°C (275°F).

Lane Joint
Cracks - Longitudinal separations along the seam
between two paving lanes.

Lift - A layer or course
of paving material applied to a base or a previous layer.

Load Equivalency Factor
- The number of 80-kN (18,000-lb.) single-axle load applications
(ESAL) contributed by one passage of an axle.

Longitudinal Crack -
A vertical Crack in the pavement that is approximately
parallel to the centerline of the pavement.

Maximum Specific
Gravity (MSG or Gmm) – The Specific Gravity
of an Asphalt Concrete mixture when that mixture has zero
Air Voids (i.e., it is in the condition of maximum Density).

Mesh
– The square openings present on the surface of
a Sieve. Sieve size is defined by the number of Mesh openings
per linear inch of the Sieve surface. For example, a No.
40 Mesh sieve has 40 openings per linear inch of Sieve
surface.

Milling Machine - A self-propelled
unit having a cutting head equipped with carbide-tipped
tools for the pulverization and removal of layers of Asphalt
paving materials from pavements. If this removed material
is reused in a new pavement, it is called RAP.

Mineral Filler - A finely
divided mineral product, at least 70 percent of which
will pass a 0.075 mm (No. 200) Sieve. Pulverized limestone
is the most commonly manufactured filler, although other
stone dust, hydrated lime, Portland Cement, and certain
natural deposits of finely divided mineral matter are
also used.

Moisture
Susceptibility – Refers to susceptibility
of an Asphalt Concrete mixture to Stripping. This property
is tested during mix design with the ITS test procedure.

Multiple Surface Treatment
- Two or more surface treatments placed one on the other.
The Aggregate maximum size of each successive treatment
is usually one-half the previous one. A Multiple Surface
Treatment may be a series of Single Surface Treatments
that produces a pavement course up to 25mm (1 in.) or
more in thickness. A Multiple Surface Treatment is a denser
waterproofing and Wearing Course than a Single Surface
Treatment.

Natural Asphalt
- Asphalt occurring in nature, which has been derived
from petroleum through natural processes of evaporation
of volatile fractions leaving the Asphalt fractions. The
native Asphalt of most importance is found in the Trinidad
and Bermudez Lake deposits. Asphalt from these sources
is often called lake Asphalt.

Non-Destructive Testing (NDT)
– Testing methods usually performed on in-place
construction materials that do not cause any damage to
the materials being tested. In the context of pavement
evaluation, NDT is Deflection testing, without destruction
to the pavement, to determine a pavement's response to
pavement loading.

Open-graded
Friction Course (OGFC) - A pavement Surface Course
that consists of a high-void, Asphalt Concrete mix that
permits rapid drainage of rainwater through the course
and off the shoulder of the road. The mixture consists
of either Polymer-modified or Rubber-modified Asphalt
Binder, a large percentage of one-sized coarse Aggregate,
and a small amount of fibers. OGFC prevents tires from
hydroplaning and provides a skid-resistant pavement surface
with significant noise reduction.

Pavement Structure
- The entire pavement system of selected materials from
Subgrade to the Surface Course.

Pay Adjustment –
The actual amount, either in dollars or in dollars per
area/weight/volume, that is to be added or subtracted
to the contractor’s bid price or unit bid price.

Performance-Graded
(PG) - Asphalt Binder grade designation used
in Superpave. It is based on the binder's mechanical performance
at critical temperatures and aging conditions.

Permeability –
A measure of the ability of a pavement to allow the passage
of air and water into or through the pavement.

Phase Angle (delta) –
Indicator of the relative amounts of recoverable (elastic)
and non-recoverable (viscous) Deformation in a material
when it is exposed to repeated pulses of Shear Stress.
For Asphalt Binder, this is highly dependent upon the
temperature and frequency of loading.

Plant Mix (Cold) - A
mixture of Emulsified (or Cutback) Asphalt Cement and
unheated mineral Aggregate prepared in a central mixing
plant and spread and compacted with conventional paving
equipment while the mixture is at or near ambient temperature.

Plant Screens - Screens
located between the Dryer and the Hot Aggregate Storage
Bins, which separate heated Aggregates into proper hot
bin sizes.

Polished Aggregate -
Aggregate particles in a pavement surface that have been
worn smooth by traffic.

Polymer – With
respect to Asphalt, a Polymer is any substance added to
Asphalt to enhance its properties. In general, a Polymer
is a material with a long-chained molecular structure,
including natural rubber, synthetic rubber, plastics,
etc.

Polymer-modified
Asphalt Binder – Asphalt Binder that has
been blended with a Polymer like styrene-butadiene block
copolymer (SBS). It has improved properties and a higher
PG-Grading compared to conventional Asphalt Binder. In
South Carolina, the SC DOT specifies PG 64-22 for conventional
Asphalt Binder and PG 76-22 for Polymer-modified Asphalt
Binder.

Portable Blending Unit or Asphalt
Rubber Blending Unit – The piece of equipment
used to blend CRM and Asphalt Binder to produce Rubber-modified
Asphalt Binder at the HMA Plant. It connects directly
to the plant and requires little or no modifications to
the plant.

Portland Cement –
A gray, powdery material that meets ASTM Standard C 150
and is composed primarily of tricalcium silicate, dicalcium
silicate, tricalcium aluminate, and tetracalcium aluminoferrite.
When combined with water, Portland Cement reacts with
the water to form a paste, which then becomes rigid as
the reaction between the cement and water progresses.

Portland Cement Concrete (PCC)
– A mixture of Portland Cement, Aggregate, water,
and other admixtures that is placed in forms and becomes
rigid as it cures. It is a commonly used construction
material in both highway and building construction.

Present Serviceability
- The ability of a specific section of pavement to serve
its intended use in its existing condition.

Pressure Aging
Vessel (PAV) – A piece of laboratory equipment
used to perform AASHTO PP1 procedure on samples of Asphalt
Binder after they have been aged in the RTFO. The PAV
further ages these binder samples by exposing them to
high pressure and temperature for 20 hours to simulate
the effects of long-term aging. PAV-aged binders are tested
with the DSR, the BBR, and the DTT.

Prime Coat - An application
of Asphalt Primer to an absorbent surface. It is used
to prepare an untreated Base Course for a Surface Course
of Asphalt Concrete. The Asphalt Primer penetrates or
is mixed into the surface of the Base Course and plugs
the voids, hardens the top, and helps bind it to the overlying
Asphalt Concrete Surface Course.

Pumping – PCC slab
Deflection under passing loads, eventually resulting in
the discharge of water and Subgrade soils along joints,
Cracks, and pavement edges.

Quality Assurance
(QA) – All those planned and systematic
actions necessary to provide confidence that a product
or facility will perform satisfactorily in service. Quality
Assurance includes Quality Control.

Quality Control (QC) or Process
Control – Those Quality Assurance actions
and considerations necessary to assess and adjust production
and construction processes so as to control the level
of quality being produced in the end product. This is
separate from Acceptance testing, but it is a part of
Quality Assurance.

Raveling
- The progressive separation of Aggregate particles in
a pavement from the surface downward or from the edges
inward.

Rebound Deflection -
The amount of surface rebound when a load is removed.

Reclaimed Asphalt Pavement (RAP)
– RAP is excavated Asphalt Concrete pavement that
has been pulverized, usually by milling, and is reused
in the production of new Asphalt Concrete paving mixtures.

Residual Asphalt Binder
- The Asphalt Binder that remains from an Asphalt Emulsion
after the Emulsifying Agent has broken and cured, or the
remains of a Cutback after the volatiles have cured.

Residual Deflection -
The difference between original and final elevations of
the pavement surface resulting from the application to,
and removal of, one or more loads from the surface.

Resiliency
– The ability of a material to resist non-recoverable
Deformation under repeated loading.

Resilient Modulus of Elasticity
- A laboratory measurement of the behavior of pavement
materials to characterize their stiffness and Resiliency.
A confined or unconfined test specimen (core or re-compacted)
is repeatedly loaded and unloaded at a prescribed rate.
The resilient modulus is a function of load duration,
load frequency, and number of loading cycles.

Rolling Thin
Film Oven (RTFO) – A piece of laboratory
equipment used to perform AASHTO T240 or ASTM D 2872 procedures
to simulate aging in Asphalt Binder samples representative
of the aging that occurs during mixing and construction
of HMA pavement. The RTFO procedure can be done to provide
samples for use in further testing or to determine the
mass lost (from lost volatiles) or gained (from the formation
of oxidation reaction products) by the binder samples
during the aging process. The RTFO ages binder samples
by continually exposing them to heat and air flow to promote
an oxidation reaction. This reaction is an accelerated
version of the aging occurring naturally in Asphalt Binders
in pavements. RTFO-aged binders may be tested with the
DSR or aged further with the PAV.

Rotational
Viscometer – A piece of laboratory equipment
used to measure the Viscosity of un-aged modified and
unmodified Asphalt Binders using the ASTM D4402 procedure.
This test may be performed at a variety of test temperatures
to gain insight into the Workability of Asphalt Concrete
mixtures containing that particular Asphalt Binder or
to develop Temperature-Viscosity Charts for the binder
being tested.

Roughometer - An instrumented,
single-wheel trailer, which measures the roughness of
a pavement surface in accumulated millimeters, or inches,
per mile.

Rubber-modified
Asphalt Binder or Asphalt Rubber Binder –
Asphalt Binder that has been blended with CRM made from
ground scrap tires at an elevated temperature to “react”
the rubber with the binder. It may be blended on-site
at the contractor’s HMA plant or terminally at the
Asphalt Binder supplier’s terminal, and it may be
used in a variety of pavement applications, including
Dense-graded HMA, Gap-graded HMA, OGFC, SAM, SAMI, and
Crack-sealant. Rubber-modified Asphalt Binder used in
different applications may contain different amounts of
CRM.

Rubber-modified
Asphalt Concrete or Rubber-modified HMA or Asphalt Rubber
Asphalt Concrete – HMA that is made with
Rubber-modified Asphalt Binder. Rubber-modified Asphalt
Concrete is produced using the Wet Process.

Rubber-tired Roller or Pneumatic-tired
Roller - A compactor used to compact various
types of Asphalt pavements with a number of rubber tires
spaced so that their tracks overlap, delivering a kneading
type of Compaction.

Rubberized Asphalt
– A broad term to describe HMA that contains CRM
made from recycled rubber. This CRM can be introduced
into the HMA by using either the Wet Process or the Dry
Process. All ARTS projects use the Wet Process.

Rubbilization - The pulverization
of a PCC pavement into smaller particles, reducing the
existing pavement layer to a sound, structural base that
will be compatible to an Asphalt Concrete Overlay.

Rutting - Channelized
depressions that develop in the wheel tracks of Asphalt
pavements resulting from consolidation under traffic loading
in one or more of the underlying pavement layers. Rutting
is not a surface problem, and usually begins in the lowest
pavement layer. It is a structural problem of insufficient
pavement strength caused by either insufficient design
pavement thickness or the weakening of an underlying pavement
layer due to moisture damage.

Sandwich Seal - A surface
treatment consisting of the application of large Aggregate,
followed by a spray-applied Asphalt Emulsion, and covered
with smaller Aggregate.

Scaling
- The peeling away or disintegrating of the surface of
PCC.

SC
DOT – South Carolina Department of Transportation

Screenings
- Fine Aggregate resulting from the rock-crushing process.

Seal
Coat – A thin surface treatment used to
improve the surface texture and protect an Asphalt pavement
surface.

Shear
Stress – the Stress resulting from the
application of forces parallel to each other, but in opposite
directions. A Shear failure is one in which the material
rips or tears as a result of the applied Shear Stress.

Shrinkage
Cracks - Interconnected Cracks forming a series
of large blocks, usually with sharp corners or angles.

Sieve
- An apparatus for laboratory work, which has a bottom
made of mesh with square openings for catching a specific
size of material. Multiple Sieves are used together to
separate material into various sizes.

Single
Surface Treatment - A single application of liquefied
Asphalt to a road surface, followed immediately by a single
layer of Aggregate. The thickness of the treatment is
about the same as the nominal maximum size Aggregate particle
used.

Skid
Resistance - The ability of a paved surface,
particularly when wet, to offer resistance to slipping
or skidding. Proper Asphalt Content, the use of Rubber-modified
Asphalt Binder, and the use of Aggregate with a rough
surface texture and high resistance to Polishing are the
greatest contributors to high Skid Resistance.

Slag
- The nonmetallic material, consisting essentially of
silicates and alumino-silicates of lime and other compounds,
that is developed simultaneously with iron in a blast
furnace. It is a byproduct of the iron manufacturing process.

Slippage
Cracks - Crescent-shaped openings in the pavement
surface resulting from traffic-induced horizontal forces
that are open in the direction of the thrust of wheels
on the pavement surface. They result when severe or repeated
Shear Stresses are applied to the surface and there is
a lack of bond between the surface layer and the course
beneath. This lack of bond can be caused by the use of
insufficient amounts of Prime or Tack, or the application
of Prime or Tack to a dirty or wet pavement surface.

Source
Properties - Aggregate characteristics that must
follow certain criteria to satisfy a Superpave mix design.
Specified values are established by local agencies. They
include Toughness, Soundness, and Deleterious Materials.

Spalling
- The breaking or chipping of a PCC pavement at joints,
Cracks, or edges, usually resulting in fragments with
featheredges.

Specific
Gravity – The ratio of the weight of a
substance compared to the weight of water when the volume
of the substance and the volume of water are exactly equal
(i.e., the Density of a substance compared to the Density
of water).

Stability
- The ability of an Asphalt Concrete mixture to resist
Deformation from imposed loads. Stability is dependent
upon both internal friction and cohesion.

Steel-wheel
Static Roller – Tandem or three-wheel roller
with cylindrical steel drums that apply their weight directly
to the pavement.

Steel-wheel
Vibratory Roller - A roller having single or
double cylindrical steel drums that perform Compaction
of pavements with weight and vibration. The amount of
compactive force is adjusted by changing the frequency
and amplitude of vibration.

Strain
– Total change in dimension divided by the original
dimension.

Stress
– Pressure (force per unit area) resulting from
the application of force.

Stripping
– The breaking of the bond between Asphalt Binder
and Aggregate in an Asphalt Concrete mixture due to the
penetration of water between the Asphalt Binder and Aggregate.
Moisture Susceptible mixes exhibit this phenomenon.

Structural
Overlay - An Asphalt Concrete Overlay constructed
for the purpose of increasing the structural value and
ride quality of the Pavement Structure.

Subbase
- The course in the Pavement Structure immediately below
the Base Course. If the Subgrade soil has adequate support,
it may serve as the Subbase.

Subgrade
- The soil prepared to support a Pavement Structure or
system. It is the foundation of the Pavement Structure.

Subgrade
Resilient Modulus - The modulus of the Subgrade
determined by repeated load, triaxial compression tests
on soil samples. It is the ratio of acceptable Axial Stress
(pressure from forces applied perpendicular to the top
and bottom surfaces of the sample) compared to recoverable
axial Strain (recoverable Deformation per unit length,
measured in the direction parallel to its vertical axis).

Superpave
– Short for "Superior Performing Asphalt Pavement",
a performance-based system for selecting and specifying
Asphalt Binders and for designing HMA mixtures that utilizes
a Gyratory Compactor for Compaction of laboratory specimens
(“pills”). It integrates the selection of
materials (Asphalt Binder and Aggregate) and Volumetric
proportioning with the project's climate and design traffic
loading.

Surface
Course – The top layer of an Asphalt Concrete
Pavement Structure.

Tack
Coat - A relatively thin application of Asphalt
Binder applied to an existing Asphalt Concrete or PCC
surface at a prescribed rate. Asphalt Emulsion is the
preferred type. It is used to form a bond between an existing
surface and the overlying Asphalt Concrete course.

Temperature
Segregation or Temperature Differential –
The existence of isolated areas of varying temperatures
in the Asphalt Mat during placement and Compaction. These
“hot spots” and “cold spots” will
exhibit different Density values than the surrounding
pavement after Compaction.

Temperature/Viscosity
Chart – A chart plotting temperature versus
Viscosity for a particular Asphalt Binder to be utilized
in the estimation of mixing and Compaction temperatures
for use in HMA mix design.

Tensile
Strength Ratio (TSR) – TSR is the ratio
between the “wet” ITS value and the “dry”
ITS value for an Asphalt Concrete mixture, expressed in
percent form. A low TSR value (below 85% for SC DOT specifications)
means that the mix lost a relatively large amount of strength
when exposed to heat and moisture, and it can probably
be considered a Moisture Susceptible mix.

Transverse
Crack - A Crack that follows a course approximately
perpendicular to the centerline of the pavement.

Truck
Factor - The number of ESALs contributed by one
passage of a vehicle. Truck Factors can apply to vehicles
of a single type or class or to a group of vehicles of
different types.

Upheaval
- The localized upward displacement of a pavement due
to swelling of the Subgrade or some portion of the Pavement
Structure.

Viscosity
– A measure of a fluid’s resistance to flow
with respect to time. The slower a fluid flows, the higher
the Viscosity. For example, molasses has a much higher
Viscosity than water.

Viscosity-Graded
- A classification system of Asphalt Cements based on
Viscosity ranges at 60°C (140°F). A minimum viscosity
at 135°C (275°F) is also usually specified. The
purpose is to prescribe limiting values of consistency
at these two temperatures. 60°C (140°F) approximates
the maximum temperature of a HMA pavement surface in service
in the U.S. 135°C (275°F) approximates the mixing
and laydown temperatures for HMA pavements.

Voids
Filled with Asphalt (VFA) - With respect to Asphalt
Concrete mixtures, the amount of Asphalt Binder, expressed
as a percentage of the VMA.

Voids
in the Mineral Aggregate (VMA) – With respect
to Asphalt Concrete mixtures, the amount of Air Voids
and Asphalt Binder, expressed as a percentage of the total
mixture volume.

Volumetric
Properties – In the context of Asphalt
Concrete mixtures, it refers to properties relating to
mixture volume, like Air Voids, VMA, VFA, MSG, and BSG.

Wearing
Course – The uppermost pavement layer forming
the surface of the pavement that is exposed to traffic
and environmental conditions. This may be a Surface Course
of Asphalt Concrete, SAM, SAMI, or any other type of surface
treatment.

Well-graded
Aggregate - Aggregate graded with relatively
uniform proportions, from the maximum size all the way
down to dust.

Wet
Grinding – A grinding method for processing
scrap tires into extremely fine crumb rubber by first
using Ambient or Cryogenic Grinding and then adding water
to form a water/rubber slurry, which is passed through
closely-spaced grinding stones. Wet Grinding produces
very fine, powdery crumb rubber particles.

Workability
- The ease with which paving mixtures may be placed and
compacted.